<!DOCTYPE html>
<html lang="en">
  <head>
    <meta charset="UTF-8" />
    <meta name="viewport" content="width=device-width, initial-scale=1.0" />
    <title>Document</title>
  </head>
  <body>
    <script>
      const arr = ["css", "html"];
      // arr = {
      //   join(){
      //     this=>arr
      //   }
      // }
      const r = arr.join.call(["a", "b"], "-");
      console.log(r);
    </script>
  </body>
</html>
